linux-kernel - RE: [PATCH v2 1/2] acpi/x86: Fix improper handling of SCI INT for platforms supporting only IOAPIC mode

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Date:   Thu, 16 Nov 2017 11:36:44 +0000
From:   "Sajjan, Vikas C" <vikas.cha.sajjan@....com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kkamagui@...il.com" <kkamagui@...il.com>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "Lakshminarasimha, Sunil Vishwanathpur" <sunil.vl@....com>,
        "Attar, Abdul Lateef" <abdul-lateef.attar@....com>
Subject: RE: [PATCH v2 1/2] acpi/x86: Fix improper handling of SCI INT for
 platforms supporting only IOAPIC mode

Thanks for review, Thomas.

-----Original Message-----
From: Thomas Gleixner [mailto:tglx@...utronix.de] 
Sent: Thursday, November 16, 2017 4:35 PM
To: Sajjan, Vikas C <vikas.cha.sajjan@....com>
Cc: rjw@...ysocki.net; rafael.j.wysocki@...el.com; linux-pm@...r.kernel.org; linux-acpi@...r.kernel.org; linux-kernel@...r.kernel.org; kkamagui@...il.com; mingo@...nel.org; Lakshminarasimha, Sunil Vishwanathpur <sunil.vl@....com>; Attar, Abdul Lateef <abdul-lateef.attar@....com>
Subject: Re: [PATCH v2 1/2] acpi/x86: Fix improper handling of SCI INT for platforms supporting only IOAPIC mode

On Thu, 16 Nov 2017, Vikas C Sajjan wrote:

Thanks for splitting this up.

> The platforms which support only IOAPIC mode and whose SCI INT is 
> greater than 16, passes SCI INT via FADT and not via MADT int src 
> override

greater? I think that's >= 16 because the legacy space is 0-15

yes, It should be >=16. Will modify it.

> structure. In such cases current logic fails to handle it and throws 
> error "Invalid bus_irq %u for legacy override".

Up to this point the changelog is informative. It just lacks the information WHY the current logic fails to handle it.

> This patch fixes it.

This part is completely useless. You should at least explain the concept of the fix, not the details (they can be seen from the code).

Sure, will remove this part.

Let me give you an example:

 Platforms which support only IOAPIC mode pass the SCI information of  interrupts above the legacy space (0-15) via the FADT mechanism and not  via MADT, i.e. the table parser ends up calling acpi_sci_ioapic_setup().

 acpi_sci_ioapic_setup() uses mp_override_legacy_irq() to register SCI  interrupts, which fails for interrupts >= 16, because it only handles  interrupts 0-15.

 Provide a separate function to handle SCI interrupts >= 16 and invoke it  conditional in acpi_sci_ioapic_setup().

 This creates some code duplication, which will be cleaned up in a separate  patch.

See?
Thanks for the example. Will give details on why the current logic fails and high level view of the fix.

> Signed-off-by: Vikas C Sajjan <vikas.cha.sajjan@....com>
> Signed-off-by: Sunil V L <sunil.vl@....com>
> Signed-off-by: Abdul Lateef Attar <abdul-lateef.attar@....com>

This Signed-off-by chain is broken. It says:

     Vikas wrote the patch and handed it to Sunil
     Sunil handed it to Abdul
     Abdul sent it to lkml

Which is obviously not the case.
3 of us worked on it, hence I had put all the 3 "Signed-off-by". Are you suggesting to call-out who did what.  Is that what you mean, when you say  "Signed-off-by chain is broken".

> ---
>  arch/x86/kernel/acpi/boot.c | 37 
> ++++++++++++++++++++++++++++++++++++-
>  1 file changed, 36 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c 
> index ef9e02e..40c24d1b 100644
> --- a/arch/x86/kernel/acpi/boot.c
> +++ b/arch/x86/kernel/acpi/boot.c
> @@ -429,6 +429,37 @@ static int mp_config_acpi_gsi(struct device *dev, u32 gsi, int trigger,
>  	return 0;
>  }
>  
> +static int __init mp_register_ioapic_irq(u8 bus_irq, u8 polarity,
> +						u8 trigger, u32 gsi)
> +{
> +	int ioapic;
> +	int pin;
> +	struct mpc_intsrc mp_irq;

I know you copied that, but please get rid of the extra line and sort the variables in reverse fir tree fashion, i.e.:

	struct mpc_intsrc mp_irq;
	int ioapic, pin;

That takes less space and is better to read/parse.
Sure, will do.
> +
> +	/*
> +	 * Convert 'gsi' to 'ioapic.pin'.
> +	 */

Please make this a one line comment. It's useful, but not that important to stand out.
OK.

> +	ioapic = mp_find_ioapic(gsi);
> +	if (ioapic < 0) {
> +		pr_warn("Failed to find ioapic for gsi : %u\n", gsi);
> +		return ioapic;
> +	}
> +
> +	pin = mp_find_ioapic_pin(ioapic, gsi);
> +
> +	mp_irq.type = MP_INTSRC;
> +	mp_irq.irqtype = mp_INT;
> +	mp_irq.irqflag = (trigger << 2) | polarity;
> +	mp_irq.srcbus = MP_ISA_BUS;
> +	mp_irq.srcbusirq = bus_irq;	/* IRQ */

Please get rid of these tail comments. First of all tail comments are disturbing the reading flow. Secondly these comment have exactly zero value.
OK.

> +	mp_irq.dstapic = mpc_ioapic_id(ioapic); /* APIC ID */
> +	mp_irq.dstirq = pin;	/* INTIN# */

except for this one, but that information should go into that other comment above, i.e.:

       /* Convert 'gsi' to ioapic.pin (INTIN#) */

Other than these more formal nitpicks, the patch is fine.
Thank you, Thomas.

Thanks,

	Tglx

Thanks 
Vikas Sajjan